"I am in seventh place."
Translation:Sono al settimo posto.
I think both translations could work, but they would have a slight different nuance.
"Sono al settimo posto" I am seventh in a ranking.
"Sono nel settimo posto" I am in the seventh place, in an existing place, not something like a ranking.
"Sono al settimo posto" is more and more and more common than your translation, anyway, since rankings are so popular on this world...